This invention relates to a phosphate supported chromium catalyst for olefin polymerization.
It has long been known to use supported chromium catalysts for olefin polymerization in either hydrocarbon solution or in a slurry system. The slurry system is preferred because of economics. However, control of molecular weight through variation in temperature is severely limited in slurry systems because the increase in temperature necessary to produce lower molecular weight (higher melt flow) material results in the polymer going into solution thus destroying the slurry process.
It has long been known broadly to use orthophosphates as supports for chromium olefin polymerization catalysts and recently improved techniques for producing aluminum phosphate catalysts have been developed which are more sensitive to molecular weight control agents. Polyphosphates such as pyrophosphates have by implication been considered inoperable in that the prior art in dealing with aluminum phosphate supports generally indicates that a phosphorus to aluminum ratio of greater than 1 is not desirable.